The invention relates to a combustion engine having at least one cylinder and a piston that is displaceable therein, the piston being connected to a crankshaft by way of a connecting rod.
While in normal reciprocating piston driving mechanisms the position of the piston in the cylinder is determined exclusively by the position of the crank, in the past it was attempted to create an option of change for different operating purposes by subdividing the connecting rod into two connecting rod parts connected to one another by way of a central joint, and further hinging a control arm to the connecting rod, the other end of the control arm being secured to the engine housing by means of a displaceable hinge point. Constructions of this type are known from, for example, DE-A-29 35 073, DE-A-29 35 977, DE-A-30 30 615, DE-A-37 15 391. In these constructions the control arm is coupled directly to the central joint, resulting in considerable problems relating to structure and operating technology. The central joint is very wide, and thus has a high weight which can no longer be balanced by counterweights on the crankshaft with the given spatial relations. Furthermore, a construction of this type is known from EP-A-0 292 603 in which the upper connecting rod part has an imaginary extension that extends beyond the central joint and whose end forms the hinge axis for the control arm. Because the distance between the axis of the central joint and the hinging for the control arm must be kept relatively small for the sake of kinematics, the structural problem resulting from the above arrangement can only be solved by means of complicated "interlacing" of the two joints. In addition to the resulting complicated and awkward structure of the joint connections, as represented for the same engine design in DE-A-43 11 865, a further disadvantage that results is that the joint becomes heavier, and the inertial forces become higher. Furthermore, it is difficult to achieve the necessary rigidity with this type of joint configuration. Moreover, this type of joint design has higher friction, which leads to measurable losses of the effective degree of efficiency.
It is known from DE-C-612 405 to hinge the control arm coaxially to the central joint on the connecting rod and to provide this hinging on the lower connecting rod part. It is also known to omit a common central joint of the upper and lower connecting rod parts and to connect the upper and lower connecting rod parts respectively to the control arm by way of a separate joint, as is known from, for example, DE-A-24 57 208 and DE-A-27 34 715. In addition to the kinematic problems of this construction, a high construction expenditure results; particularly when the central joint between the upper and lower connecting rod parts is omitted, very unfavorable stress conditions result for the components of the piston drive formed by the above, particularly for the control arm.
The object of the invention is to avoid the disadvantages with respect to structure and operating technology of the known structural shapes discussed above.